1. Field of the Invention
The present invention relates to a scanning apparatus for conducting a two-dimensional scanning.
2. Description of the Prior Art
In usual two-dimensional scanning with a light beam there are employed a pair of deflectors provided with reflecting surfaces, wherein a first deflector with a constant angular velocity deflects an incident light beam into a first direction, while a second deflector with a constant angular velocity receives thus deflected light beam and deflects said beam into a second direction perpendicular to said first direction, the light beam thus deflected two-dimensionally being focused by an imaging lens of a distortion characteristic y=f.multidot..theta. thereby achieving a two-dimensional scanning. In such conventional two-dimensional light beam scanning apparatus, said first and second deflectors are located close to each other since otherwise the reflecting surface of second deflector has to be made larger in order to receive the light beam deflected by the first deflector when the deflecting angle thereof is increased. Also the focusing of the light beam deflected by said first and second deflectors onto the scanning surface is achieved by a lens with a distortion characteristic of y=f.multidot..theta. because the light beam, subjected to the deflections generally of constant angular velocities in said first and second deflectors, will not provide a displacement linear in time on the scanning surface if focused by a lens with a distortion characteristic of y=f.multidot.tan .theta., for example an ordinary photographic lens.
In this foregoing equations, f indicates the focal length of imaging lens, and .theta. is the angle formed between the optical axis of said lens and the incident light beam thereto.